Always use the graceful method unless absolutely necessary. i.e don’t just yank the power cord out.
Graceful method with physical access to device with no console: Press and immediately release the Power button. The device begins gracefully shutting down the operating system and then powers itself off
Graceful method while logged in via terminal or console (CLI method):
root@srx320> request system power-off Power Off the system ? [yes,no] (no) yes Shutdown NOW! [pid 2480] root@srx320> *** FINAL System shutdown message from root@gandalf *** System going down IMMEDIATELY Sep 6 19:28:19 init: l2-learning (PID 1719) exited with status=0 Normal Exit Sep 6 19:28:19 init: routing (PID 1718) exited with status=0 Normal Exit Sep 6 19:28:19 init: mib-process (PID 1717) exited with status=0 Normal Exit SWaiting (max 60 seconds) for system process `vnlru' to stop...done Waiting (max 60 seconds) for system process `vnlru_mem' to stop...done Waiting (max 60 seconds) for system process `bufdaemon' to stop...done Waiting (max 60 seconds) for system process `syncer' to stop... Syncing disks, vnodes remaining...0 0 0 0 done syncing disks... Syncing disks, buffers remaining... 6 6 6 6 6 3 3 3 3 3 3 3 1 1 1 1 1 1 1 Final sync complete Uptime: 1h27m5s The operating system has halted. Turning the system power off.
Forced shutdown with physical access to device with no console: Press the Power button and hold it for 10 seconds. The device immediately powers itself off without shutting down the operating system.
A more complete guide on syntax and options: